Circuit for detecting transmission bus's abnormality and for controlling output drivers in a complementary signal transmission device

Abstract

There is disclosed a two-wire input/output device with an object of avoiding that communication becomes impossible when an abnormality occurs on one of two-wire LAN transmission lines. A pair of buses are separately controlled by driver circuits. An abnormality on a transmission line is detected by an abnormality detecting circuit with data supplied to terminals, and driving of only one of the driver circuits which corresponds to the bus having the abnormality is stopped by an output control circuit. When an abnormality occurs on one of the transmission lines, communication is enabled with a driver circuit corresponding to the transmission line having the abnormality being protected.

What is claimed is: 
     
       1. A two-wire input/output device connected to a first and a second transmission lines on which a first and a second signals with phases opposite to each other are transmitted, respectively, comprises: (a) a first and a second driver circuits for supplying said first and second signals to said first and second transmission lines, respectively;   (b) an input circuit receiving said first and second signals for generating a first comparison signal obtained by comparing said first signal and a predetermined potential, a second comparison signal obtained by comparing said second signal and said predetermined potential and a third comparison signal obtained by comparing said first signal and said second signal;   (c) a reset circuit receiving said third comparison signal for generating a reset signal which is activated when said first and second transmission lines are normal;   (d) an abnormality detecting circuit receiving said first and second comparison signals and said reset signal for generating a first and a second error signals which are activated when an abnormality occurs on one of said first and second transmission lines, respectively; and   (e) an output control circuit receiving input data on which said first and second signals are based and said first and second error signals for stopping driving of said first and second driver circuits respectively when one of said first and second error signals is active and driving said first and second driver circuits according to said input data when said first and second error signals are inactive.   
     
     
       2. The two-wire input/output device according to claim 1, wherein said output control circuit comprises; (e-1) a first T flip-flop receiving said first error signal to be reset and receiving said input data as a trigger signal,   (e-2) a second T flip-flop receiving said second error signal to be reset and receiving said input data as a trigger signal,   (e-3) a first gate for supplying to said first driver circuit a signal which is an inversion of a logical product of an output of said first T flip-flop and said input data, and   (e-4) a second gate for supplying to said second driver circuit a signal which is an inversion of a logical product of an output of said second T flip-flop and said input data.   
     
     
       3. The two-wire input/output device according to claim 2, wherein said first driver circuit comprises; (a-1) a first potential point, and   (a-2) a first transistor having a first current electrode connected to said first potential point, a second current electrode connected to said first transmission line and a control electrode connected to said output control circuit, and said second driver circuit comprises;     (a-3) a second potential point, and   (a-4) a second transistor having a first cur;rent electrode connected to said second potential point, a second current electrode connected to said first transmission line and a control electrode connected to said output control circuit.   
     
     
       4. The two-wire input/output device according to claim 1, wherein said reset circuit further produces an auxiliary reset signal which is not related to said third comparison signal, and said abnormality detecting circuit includes; (d-1) a first counter which counts said first comparison signal and is reset by said reset signal,   (d-2) a first D flip-flop which inputs an output of said first counter as trigger and is reset by said auxiliary reset signal,   (d-3) a second counter which counts said second comparison signal and is reset by said reset signal, and   (d-4) a second D flip-flop which inputs an output of said second counter as trigger and is reset by said auxiliary reset signal.   
     
     
       5. The two-wire input/output device according to claim 4, wherein said reset circuit includes (c-2) a power-supply reset circuit which operates with reset of a power-supply and produces said auxiliary reset signal. 
     
     
       6. The two-wire input/output device according to claim 5, wherein said reset circuit further includes; (c-3) a gate for reset taking a logical product of an external reset signal supplied from outside of said reset circuit and an output of said power-supply reset circuit to produce said auxiliary reset signal.   
     
     
       7. The two wire input/output device according to claim 1, wherein said abnormality detecting circuit includes; (d-5) a gate for error signal for taking a logical sum of said first and second error signals to produce a third error signal, and   (d-6) a latch circuit for latching said third error signal and producing a fourth error signal.   
     
     
       8. The two-wire input/output device according to claim 7, wherein said latch circuit comprises a D flip-flop having a D input end fixed to a potential corresponding to predetermined logic, a T input end for inputting said third error signal and an inversion output end for outputting said fourth error signal. 
     
     
       9. A two-wire input/output device connected to a first and a second transmission lines on which a first and a second signals with phases opposite to each other are transmitted, respectively, comprises: (a) a driver circuit for supplying said first and second signals to said first and second transmission lines, respectively,   (b) an input circuit receiving said first and second signals for producing a first comparison signal obtained by comparing said first signal and a predetermined potential, a second comparison signal obtained by comparing said second signal and said predetermined potential and a third comparison signal obtained by comparing said first signal and said second signal;   (c) a reset circuit receiving said third comparison signal for producing a reset signal which is activated when said first and second transmission lines are normal;   (d) an abnormality detecting circuit receiving said first and second comparison signals and said reset signal for producing an error signal which is activated when an abnormality occurs on one of said first and second transmission lines, respectively;   (e) an output control circuit receiving input data on which said first and second signals are based and said error signal for stopping driving of said driver circuit in principle when said error signal is active and for driving said driver circuit according to said input data when said error signal is inactive; and   (f) a timer receiving said error signal to be started with its activation for supplying a special driving signal after a certain period from said activation of said error signal to said output control circuit to make said output control circuit drive said driver circuit as an exception even if said error signal is active.   
     
     
       10. The two-wire input/output device according to claim 9 wherein said timer is a programmable timer. 
     
     
       11. The two-wire input/output device according to claim 9, wherein said error signal is single, said timer is single, and   said special driving signal is single,   
     
     
       12. The two-wire input/output device according to claim 11, wherein said output control circuit comprises; (e-1) a first output gate for taking logical product of an inversion signal of said error signal and said input data, and   (e-2) a second output gate for taking inversion of a logical sum of an output of said first output gate and said special driving signal and supplying to said diver circuit,   
     
     
       13. The two-wire input/output device according to claim 9, wherein said error signal forms a pair,   said timer forms a pair and supplies a pair of said special driving signals to said output control circuit, and   said reset circuit further receives said first and said second comparison signals and, respectively, on the basis of each of the same, outputs a first and a second auxiliary reset signals for resetting said pair of timers together with said pair of error signals.   
     
     
       14. The two-wire input/output device according to claim 13, wherein one of said timers comprises; (f-1) a first gate for timer for outputting logical product of one of said special driving signal and logical inversion of one of said error signals, and   (f-2) a first timer element which is reset by output of said first gate for timer for outputting one of said special driving signal, and     the other one of said timers comprises; (f-3) a second gate for timer for outputting logical product of the other one of said special driving signals and logical inversion of the other one of said error signals, and   (f-4) a second timer element which is reset by an output of said second gate for timer for outputting the other one of said special driving signal.     
     
     
       15. The two-wire input/output device according to claim 9, wherein said error signal formes a pair,   said timer forms a trio and supplies a trio of said special driving signals to said output control circuit, and   said reset circuit further receives said first and second comparison signals and, respectively, on the basis of the same, outputs a first and a second auxiliary reset signals for resetting said trio of timers together with said pair of error signals.   
     
     
       16. A two-wire input/output device connected to a first and a second transmission lines on which a first and a second signals with phases opposite to each other are transmitted, respectively, comprises: (a) a first and a second driver circuits for supplying said first and second signals to said first and second transmission lines, respectively;   (b) an input circuit receiving said first and second signals for producing a first comparison signal obtained by comparing said first signal and a predetermined potential, a second comparison signal obtained by comparing said second signal and said predetermined potential and a third comparison signal obtained by comparing said first signal and said second signal;   (c) a reset circuit receiving said third comparison signal for producing a reset signal which is activated when said first and second transmission lines are normal;   (d) an abnormality detecting circuit having, (d-1) a first counter which is reset by said reset signal and counts said second comparison signal to output a first count output,   (d-2) a first D flip-flop which inputs said first count output as trigger and is reset by said reset signal for producing a first error signal which is activated when an abnormality occurs on said first transmission line,   (d-3) a second counter which is reset by said reset signal for counting said first comparison signal to output a second count output, and   (d-4) a second D flip-flop which inputs said second count output as trigger and is reset by said reset signal for producing a second error signal which is activated when an abnormality occurs on said second transmission line; and     (e) an output control circuit (e-1) receiving input data on which said first and second signals are based and said first and second error signals,   (e-2) for driving said driver circuit according to said input data when said first and second error signals are inactive, and   (e-3) for stopping driving of said first and second driver circuits in principle, when one of said first and said second error signals is active, respectively, and driving said first and second driver circuits as an exception when said first count output and said second count output attain predetermined value, respectively.     
     
     
       17. The two-wire input/output device according to claim 16, wherein, in said abnormality detecting circuit, said first and second counters include two T flip-flops respectively connected in series. 
     
     
       18. The two-wire input/output device according to claim 16, wherein said first and second counters in said abnormality detecting circuit include three T flip-flops respectively connected in series. 
     
     
       19. The two-wire input/output device according to claim 16, wherein said abnormality detecting circuit further comprises a gate for error signal for producing a third error signal by taking a logical sum of said first and second error signals, and   said reset circuit further receives said third error signal, and comprises (c-1) a counter for reset which counts said third comparison signal as trigger and is reset by said third error signal.   
     
     
       20. A two-wire input/output device connected to a first and a second transmission lines on which a first and a second signals with phases opposite to each other are transmitted, respectively, comprises: (a) a driver circuit for supplying said first and second signals to said first and second transmission lines, respectively;   (b) an input circuit receiving said first and second signals for producing a first and a second reference signals respectively indicating whether said first and second signals are normal or not;   (c) an abnormality detecting circuit receiving said first and second reference signals for producing an error signal which is activated when an abnormality occurs on one of said first and second transmission lines;   (d) an output control circuit receiving input data on which said first and second signals are based and said error signal for stopping driving of said driver circuit when said error signal is active and driving said driver circuit according to said input data when said error signal is inactive; and   said abnormality detecting circuit having (c-1) a coincidence detecting circuit for producing a coincidence detection signal which is activated when said first and second reference signals do not coincide with each other, and   (c-2) a coincidence detection holding circuit for holding said coincidence detection signal and producing said error signal.     
     
     
       21. The two-wire input/output device according to claim 20, wherein said input circuit comprises; (b-1) a reference potential point for supplying a reference potential,   (b-2) a first comparator for comparing said first signal and said predetermined potential to obtain said first reference signal, and   (b-3) a second comparator for comparing said second signal and said predetermined potential to obtain said second reference signal.   
     
     
       22. The two-wire input/output device according to claim 21, wherein said coincidence detecting circuit includes (c-1-1) a gate for abnormality detection for outputting inversion of exclusive logical sum of said first and second reference signals. 
     
     
       23. The two-wire input/output device according to claim 22, wherein said coincidence detection holding circuit comprises; (c-2-1) a one-shot monostable multivibrator provided with said coincidence detection signal as trigger for outputting a pulse signal,   (c-2-2) a first D flip-flop having a D input end supplied with said coincidence detection signal, a trigger input end supplied with said pulse signal and a non-inversion output end, and   (c-2-3) a second D flip-flop having a D input end supplied with potential corresponding to predetermined logic, a trigger input end connected to said non-inversion output end of said first D flip-flop and a non-inversion output end for outputting said error signal.   
     
     
       24. The two-wire input/output device according to claim 21, wherein said coincidence detection holding circuit includes; (c-2-4) a filter receiving said coincidence detection signal for outputting a corrected coincidence detection signal by removing frequency component higher than basic frequency of said first and second reference signals therefrom, and   (c-2-5) a D flip-flop having a D input end supplied with potential corresponding to predetermined logic, a trigger input end supplied with said corrected coincidence detection signal and a non-inversion output end for outputting said error signal.   
     
     
       25. The two-wire input/output device according to claim 21 wherein said coincidence detection holding circuit comprises; (c-2-6) a filter receiving said coincidence detection signal and outputting a corrected coincidence detection signal by removing frequency component higher than basic frequency of said first and second reference signals therefrom,   (c-2-7) a one-shot monostable multivibrator supplied with said corrected coincidence detection signal as trigger and having an output end for outputting a pulse signal,   (c-2-8) an abnormality detecting gate for outputting logical product of an output of said one-shot monostable multivibrator and said corrected coincidence detection signal,   (c-2-9) an oscillator for outputting an oscillation signal having basic frequency higher than the basic frequency of said first and second reference signals,   (c-2-10) a first D flip-flop having a D input end supplied with an output of said abnormality detecting gate, a trigger input end supplied with said oscillation signal and a non-inversion output end, and   (c-2-11) a second D flip-flop having a D input end supplied with potential corresponding to predetermined logic, a trigger input end connected in common to said output end of said one-shot monostable multivibrator and said non-inversion output end of said first D flip-flop and a non-inversion output end for outputting said error signal.   
     
     
       26. The two-wire input/output device according to claim 20, wherein said input circuit comprises, (b-4) a first gate for inverting said first signal to obtain said first reference signal, and   (b-5) a second gate for holding the logic of said second signal and obtaining said second reference signal.   
     
     
       27. The two-wire input/output device according to claim 26, wherein said coincidence detection holding circuit includes; (c-2-12) a one-shot monostable multivibrator supplied with said coincidence detection signal as trigger for outputting a pulse signal,   (c-2-13) a first D flip-flop having a D input end supplied with said coincidence detection signal and a trigger input end supplied with said pulse signal, and   (c-2-14) a second D flip-flop having a D input end supplied with potential corresponding to predetermined logic and a trigger input end supplied with an output of said first D flip-flop for outputting said error signal.   
     
     
       28. A two-wire input/output device connected to a first and a second transmission lines on which a first and a second signals with phases opposite to each other are transmitted, respectively, comprising: (a) a driver circuit for supplying said first and second signals to said first and second transmission lines, respectively;   (b) an input circuit receiving said first and second signals for producing a first and a second reference signals respectively indicating whether said first and second signals are normal or not;   (c) an abnormality detecting circuit receiving said first and second reference signals for producing an error signal which is activated when an abnormality occurs on one of said first and second transmission lines;   (d) an output control circuit receiving input data on which said first and second signals are based and said error signal for stopping driving of said driver circuit when said error signal is active and driving said driver circuit according to said input data when said error signal is inactive; and   said abnormality detecting circuit having; (c-1) a first one-shot multivibrator receiving said first reference signal as trigger and outputting a signal in the form of pulse,   (c-2) a second one-shot multivibrator receiving a signal obtained by inverting said first reference signal as trigger and outputting a signal in the form of pulse,   (c-3) a third one-shot multivibrator receiving said second reference signal as trigger and outputting a signal in the form of pulse,   (c-4) a fourth one-shot multivibrator receiving a signal obtained by inverting sad second reference signal as trigger and outputting a signal in the form of pulse, and   (c-5) a gate for abnormality detection for taking a logical sum of outputs of said first through fourth one-shot multivibrators to produce said error signal.     
     
     
       29. The two-wire input/output device according to claim 28, wherein said input circuit comprises; (b-1) a reference potential point for supplying a reference potential,   (b-2) a first comparator for comparing said first signal and said predetermined potential to obtain said first reference signal, and   (b-3) a second comparator for comparing said second signal and said predetermined potential to obtain said second reference signal.